i have flown both 3 and 4 channel planes and i don't really see that much difference in them as a beginning plane as long as you start with a 4 channel radio. for 3 channels, instead of putting the rudder on the rudder channel, i use the aileron channel so that when my students move up to aileron planes, they don't feel it is so different. of course most people will argue that this breeds bad habits (not using the rudder) but 3 channel electrics are just cheaper. plus, with the super dihedral of rudder setups, they are great for teaching new students. it works just like that pilot assist by righting the aircraft. in fact, it's hard to fly inverted for long with rudder setups.

so for basic teaching and flying, rudder may be even easier to learn than aileron. for basic aerobatics, however, while there are aerobatics you can do with a rudder only set up, aileron set up is significantly better.

so in a nutshell, 3-channel (rudder) may get you started faster, you will be able to grow more with the 4-channel (w/aileron) set up.